The present invention relates to a nitride semiconductor device where a nitride semiconductor is used as an active layer and a manufacturing method for the same, and in particular, to a nitride semiconductor device having an ohmic electrode that makes ohmic contact with the semiconductor device, such as a high electron mobility transistor (HEMT) and a field effect transistor (FET), and a manufacturing method thereof.
FIG. 4 is a cross sectional diagram of a semiconductor device made of a conventional III-V group nitride semiconductor. The semiconductor device shown in FIG. 4 has a so-called HEMT structure where a buffer layer 102 made of gallium nitride (GaN), a channel layer 103 made of gallium nitride, a charge supply layer 104 made of n type aluminum gallium nitride (AlGaN) and a Schottky layer 105 made of undoped aluminum gallium nitride are sequentially deposited on a substrate 101 made of a sapphire substrate, where a two-dimensional electron gas layer made of a potential well and having an extremely high electron mobility is formed in the vicinity of the interface where the channel layer 103 and the charge supply layer 104 form a hetero junction. In the semiconductor device having such a structure, a voltage that is applied to a gate electrode 106 (control electrode) that makes Schottky contact with the Schottky layer 105 is controlled, and thereby, carriers (two-dimensional electron gas) that flow between a source electrode 107a and a drain electrode 107b (ohmic electrode) are controlled. As described above, in the conventional semiconductor device, the source electrode 107a and the drain electrode 107b are formed on the Schottky layer 105 made of undoped aluminum gallium nitride.
In the semiconductor device of this type, there have been proposed various structures disclosed in, for example, Japanese Unexamined Patent Publication No. 335637/1998, in addition to the above described structure.